Protein kinase C reduces the KCa current of rat tail artery smooth muscle cells.

The hypothesis that protein kinase C (PKC) is able to regulate the whole cell Ca-activated K (KCa) current independently of PKC effects on local Ca release events was tested using the patch-clamp technique and freshly isolated rat tail artery smooth muscle cells dialyzed with a strongly buffered low-Ca solution. The active diacylglycerol analog 1,2-dioctanoyl- sn-glycerol (DOG) at 10 μM attenuated the current-voltage ( I- V) relationship of the KCa current significantly and reduced the KCacurrent at +70 mV by 70 ± 4% ( n = 14). In contrast, 10 μM DOG after pretreatment of the cells with 1 μM calphostin C or 1 μM PKC inhibitor peptide, selective PKC inhibitors, and 10 μM 1,3-dioctanoyl- sn-glycerol, an inactive diacylglycerol analog, did not significantly alter the KCa current. Furthermore, the catalytic subunit of PKC (PKCC) at 0.1 U/ml attenuated the I- Vrelationship of the KCa current significantly, reduced the KCacurrent at +70 mV by 44 ± 3% ( n = 17), and inhibited the activity of single KCa channels at 0 mV by 79 ± 9% ( n = 6). In contrast, 0.1 U/ml heat-inactivated PKCC did not significantly alter the KCacurrent or the activity of single KCa channels. Thus these results suggest that PKC is able to considerably attenuate the KCa current of freshly isolated rat tail artery smooth muscle cells independently of effects of PKC on local Ca release events, most likely by a direct effect on the KCa channel.